This application claims the priority of German Application No. 198 46 026.0, filed Oct. 6, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a regulating device for a refrigerant circuit of an air conditioner, especially a vehicle air conditioner, with the refrigerant circuit being divided by a compressor and a vent element into a high-pressure side and a low-pressure side. A control part on the high-pressure side controls one or more high-pressure-side air conditioning components that can be controlled. A low-pressure-side control part controls one or more low-pressure-side air conditioner components that can be controlled.
The refrigerant circuit of an air conditioner, as used especially in motor vehicles, is usually divided into a high-pressure side and a low-pressure side by a compressor and a vent element, such as a controllable expansion valve or single or multistage fixed throttle. In the refrigerant flow direction, the high-pressure side begins on the compressor outlet side and extends up to the inlet side of the expansion element. The low-pressure side begins on the outlet side of the expansion element and extends up to the intake, in other words the input side of the compressor. On the high-pressure side and on the low-pressure side, there are one or more air conditioner components that can be controlled. For example, the compressor and the expansion valve can be controlled, as well as air flow control devices, such as a fan and/or air flaps associated with a condenser on the high-pressure side and/or an evaporator on the low-pressure side.
Recently, the use of refrigerant R 744, in other words carbon dioxide, instead of the conventional refrigerants R 134a and R 12 has been considered even for motor vehicle air conditioners; see the article by H. Gentner and A. Foldi, "Carbon Dioxide as Refrigerant for Automobile Air Conditioners" in Ki Luft und Kaltetechnik, No. 1, 1998, p. 19. The cooling unit connected downstream of the compressor is referred to in these carbon dioxide systems not as a condenser, as in the case of the conventional refrigerants mentioned above, but as a gas cooler. This is because the low critical temperature of CO2 means that it frequently operates in the supercritical range and therefore causes no condensation. Because of the frequently supercritical operation and the high operating pressures that develop, special requirements apply to carbon dioxide air conditioners, including their control.
Within the scope of a European "project" RACE referred to in the article cited above, a regulating device was proposed for a CO2 refrigerant circuit that incorporates a high-pressure-side control part and a low-pressure-side control part independent thereof. The regulating part on the high-pressure side has a regulating circuit for controlling an expansion valve at a high-pressure setpoint, which is set using the coefficient of performance control, with the term "coefficient of performance" (abbreviated COP) referring to the ratio of the cooling power to the effective driving power of the system. COP regulation determines the high-pressure setpoint as a function of the air temperature on the air-inlet side of the gas cooler. The regulating part on the low-pressure side incorporates a control circuit for regulating the compressor to a specific intake pressure setpoint. An evaporator temperature regulating circuit is superimposed on this compressor intake pressure control circuit and adjusts the intake pressure setpoint as a function of the control deviation of the evaporator temperature.
The technical problem solved by the invention is the provision of a refrigerant circuit control device of the type recited at the outset with which air conditioners, especially those with a controllable compressor and possibly also a controllable expansion valve (and especially also CO2 air conditioners), can be regulated at relatively low control-technology expense, saving energy and functioning comparatively precisely and stably with high efficiency.
The invention solves this problem by providing a control device for a refrigerant circuit of an air conditioner, especially a vehicle air conditioner, with the refrigerant circuit being divided by a compressor and a vent element into a high-pressure side and a low-pressure side. A control part on the high-pressure side controls one or more high-pressure-side air conditioning components that can be controlled. A low-pressure-side control part controls one or more low-pressure-side air conditioner components that can be controlled. The two control parts are coupled with one another, with at least one influential parameter of the one control part forming a coupling parameter that is coupled into the other control part (to form an influential parameter there as well).
In this control device according to the invention, the high-pressure-side and low-pressure-side controlling parts are coupled together because at least one influential parameter of one regulating part forms a coupling parameter that is coupled into the other control part as an influential parameter that is operative there as well. The term "influential parameter" refers to all those physical parameters that influence the controlling behavior of the regulating section in question, in other words which are set by the control components or are supplied to the latter. For the sake of simplicity, in this context the term "control" will also be understood to include pure control interventions, i.e., interventions without feedback. Due to the coupling of the two regulating parts, they can operate adjusted to one another, so that a desired control behavior of the air conditioner can be achieved reliably and with a stable control behavior, for example the achievement of a desired evaporator temperature. It turns out that CO2 air conditioners in particular can also be regulated satisfactorily in this manner, so that energy-saving operation is possible especially also in the low power range with a suitable system design, so that a comparatively high total efficiency is achieved.
In an advantageous control device according to the invention, a low-pressure-side influential parameter forms a regulating variable for a low-pressure-side compressor intake pressure regulator or a low-pressure-side evaporator temperature regulator and serves as a coupling parameter coupled into the control part on the high-pressure side.
In a further advantageous control device according to the invention, the influential parameter is a low-pressure side influential parameter coupled to the high-pressure-side control part and serves on the high-pressure side as an influential parameter to adjust the setpoint for a high-pressure regulator and/or to adjust the power of a fan for a cooling unit connected downstream of the compressor, such as a condenser or gas cooler.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.